全文获取类型
收费全文 | 406034篇 |
免费 | 4485篇 |
国内免费 | 1709篇 |
专业分类
电工技术 | 6811篇 |
综合类 | 2843篇 |
化学工业 | 56477篇 |
金属工艺 | 20380篇 |
机械仪表 | 16000篇 |
建筑科学 | 9307篇 |
矿业工程 | 2698篇 |
能源动力 | 8520篇 |
轻工业 | 26066篇 |
水利工程 | 4823篇 |
石油天然气 | 7348篇 |
武器工业 | 43篇 |
无线电 | 46623篇 |
一般工业技术 | 84731篇 |
冶金工业 | 57478篇 |
原子能技术 | 8582篇 |
自动化技术 | 53498篇 |
出版年
2021年 | 2151篇 |
2019年 | 2063篇 |
2018年 | 22576篇 |
2017年 | 22167篇 |
2016年 | 15974篇 |
2015年 | 3409篇 |
2014年 | 4611篇 |
2013年 | 12162篇 |
2012年 | 11628篇 |
2011年 | 24201篇 |
2010年 | 20799篇 |
2009年 | 18916篇 |
2008年 | 19905篇 |
2007年 | 22310篇 |
2006年 | 7955篇 |
2005年 | 11285篇 |
2004年 | 9667篇 |
2003年 | 9236篇 |
2002年 | 7673篇 |
2001年 | 6973篇 |
2000年 | 6736篇 |
1999年 | 6820篇 |
1998年 | 16339篇 |
1997年 | 11603篇 |
1996年 | 8959篇 |
1995年 | 6859篇 |
1994年 | 6046篇 |
1993年 | 6081篇 |
1992年 | 4414篇 |
1991年 | 4225篇 |
1990年 | 4073篇 |
1989年 | 4055篇 |
1988年 | 3759篇 |
1987年 | 3387篇 |
1986年 | 3392篇 |
1985年 | 3739篇 |
1984年 | 3460篇 |
1983年 | 3217篇 |
1982年 | 3024篇 |
1981年 | 3038篇 |
1980年 | 3030篇 |
1979年 | 2829篇 |
1978年 | 2869篇 |
1977年 | 3141篇 |
1976年 | 4098篇 |
1975年 | 2416篇 |
1974年 | 2379篇 |
1973年 | 2396篇 |
1972年 | 2018篇 |
1971年 | 1781篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
In this work was investigated the effect of the addition of barium titanate (BaTiO3) on electrical properties of two chemically recyclable thermosets, polyhemiaminal (PHA) and polyhexahydro‐s‐triazine (PHT), both fabricated from 4,4′‐oxydianiline (ODA), an ether derivative of aniline and paraformaldehyde. Thermal and mechanical properties as well as chemical recyclability of the two polymers and their nanocomposites/nanodielectrics were also investigated. In addition, a quantitative analysis was conducted of the nanoparticle dispersion in the PHA‐/PHT‐based BaTiO3‐containing nanocomposites using transmission electron microscopy imaging and the nearest‐neighbor distance index and this index was used to analyze the investigated properties in connection with the proper mechanisms. Regarding the electrical properties for both neat polymers, conductivity values of the order of 10?8 S m?1 at 100 Hz were observed and dielectric constant values close to 2.80 for both polymers at 1 kHz. The addition of 0.5 wt% of BaTiO3 ferroelectric nanoparticles increased by about 44% the dielectric constant (1 kHz) and conductivity (102 Hz) of the PHA‐based nanocomposite. PHA and PHT exhibited glass transition temperature (Tg) values in the range 125–180 °C. An increase of 7 °C in Tg was observed after the incorporation of 0.5 wt% of BaTiO3 into PHA. Concerning the mechanical properties, values in the range 4.00–4.45 GPa for reduced modulus and 0.30–0.43 GPa for nanohardness for PHA and PHT polymers were observed. Independently of filler content or polymer matrix, both mechanical properties were enhanced after the addition of BaTiO3. The chemical recycling of PHA/PHT and all nanocomposites in the initial ODA reagent after sulfuric acid treatment was successfully characterized using the NMR and Fourier transform infrared spectroscopic techniques. © 2018 Society of Chemical Industry 相似文献
62.
Akopdzhanyan T. G. Chemagina E. A. Borovinskaya I. P. 《Russian Journal of Non-Ferrous Metals》2020,61(6):686-690
Russian Journal of Non-Ferrous Metals - The synthesis and sintering of the (AlN)x(SiC)1 – x solid solution have been studied under conditions of self-propagating high-temperature synthesis... 相似文献
63.
Madhu H. C. Edachery Vimal Lijesh K. P. Perugu Chandra Shekhar Kailas Satish V. 《Metallurgical and Materials Transactions A》2020,51(8):4086-4099
Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result... 相似文献
64.
Zavadiuk S.V. Loboda P.I. Soloviova T.O. Trosnikova I.Iu. Karasevska O.P. 《Powder Metallurgy and Metal Ceramics》2020,59(1-2):22-28
Powder Metallurgy and Metal Ceramics - The properties of sintered and heat-treated steels produced from the Catamold 8740 material by powder injection molding were examined. Parts made of the... 相似文献
65.
66.
67.
Marcela Stoia Cornelia Păcurariu Ciprian Mihali Iosif Mălăescu Cătălin Nicolae Marin Aylin Căpraru 《Ceramics International》2019,45(2):2725-2735
Magnetic MnFe2O4 nanopowders were synthesized by an original solvothermal method in the absence and in the presence of tetra-n-butylammonium bromide (TBAB) and Tween 80 (TW) as surfactants. Manganese ferrite/polyaniline (PANI) hybrid materials were synthesized by in situ polymerization of aniline on the surface of MnFe2O4 using ammonium persulfate as oxidant. The purpose of the study was to investigate the influence of the two surfactants on the properties of the MnFe2O4 powders and of their composites with PANI. The specific surface area, the cumulative surface area of pores and the cumulative volume of pores are influenced by the nature of surfactant in case of MnFe2O4 powders and are higher by comparison to those of the MnFe2O4/PANI hybrid materials. The values of saturation magnetization in case of MnFe2O4 powders are higher than those of the hybrid materials and are not influenced by the surfactant nature. These features revealed that MnFe2O4 powders can be efficiently used as adsorbents for the purification of wastewaters. The values of the electrical conductivity of the composites exhibit a significant increase in comparison to the MnFe2O4 powders and depend on the surfactant nature. The highest value of electrical conductivity was achieved by the composite obtained using Tween 80 as surfactant (σDC = 54.5·10?5S?m?1) which was close to that of PANI (σDC = 61.2·10?5 S?m?1). The fact that the magnetic and electric properties of the synthesized MnFe2O4/PANI composites can be changed by design, demonstrate the high potential of these materials to be used in magneto-electric applications. 相似文献
68.
69.
70.